CT6944 Hastelloy G3 rods and Hastelloy G3 bars

Hastelloy G3 Rods/Bars Description

Hastelloy G3 (UNS N06985) is a nickel-based face‐centred cubic (FCC) γ‐austenitic alloy. Its microstructure comprises a primary Ni-Cr-Mo-Fe solid-solution matrix reinforced by M₆C/M₂₃C₆ carbides (≤0.5 vol%) and coherent Ni₃(Ti, Al) γ' precipitates. The alloy exhibits stable passivation behaviour via the formation of Cr₂O₃/MoO₂ oxide layers, thereby providing resistance to reducing acids (e.g. sulphuric acid ≤50% up to 90°C) and localised corrosion (critical pitting temperature >85°C in 6% FeCl₃). Copper improves sulphuric acid resistance and inhibits dezincification.

Thermally, the alloy maintains phase stability up to 1040°C with negligible σ-phase precipitation below 650°C. Its coefficient of thermal expansion (CTE) is 14.2 μm/m·°C (20–400°C), and thermal conductivity increases from 8.9 W/m·K (20°C) to 19.2 W/m·K (600°C). Mechanically, the annealed condition provides a tensile strength ≥790 MPa, a yield strength ≥355 MPa, and an elongation ≥40%, while retaining >85% yield strength at 400°C. The fracture toughness (Kᵢc) is greater than 200 MPa√m as a result of dislocation cross‐slip in the FCC lattice.

Electrochemically, the alloy exhibits a corrosion rate of <0.1 mm/year in phosphoric acids (≤85%) and in chloride/sulphide brines (pH ≥1.5) due to the formation of MoOₓ-rich passive films. Its ductile-to-brittle transition temperature (DBTT) remains below –100°C, attributable to the inherent toughness of nickel. Surface films display a high impedance (>10⁵ Ω·cm²) in electrochemical noise testing, thereby confirming barrier integrity.

Hastelloy G3 Rods/Bars Applications

Hastelloy G3 rods/bars are used in industrial settings that involve exposure to corrosive media. In chemical processing, they are employed to fabricate reactors, heat exchangers and piping systems for sulphuric acid (≤50% concentration), phosphoric acid (≤85%) and mixed acid media, given that they perform according to quantitative evaluations of general corrosion and stress corrosion cracking (SCC). The petrochemical sector utilises these products for downhole components (e.g. valve stems, pump shafts) in sour gas wells containing H₂S/CO₂/Cl⁻ brines, where a molybdenum content exceeding 6.5% is effective in preventing pitting.

In pollution control, Hastelloy G3 bars are machined to produce absorber modules and ductwork in flue gas desulphurisation (FGD) systems, thereby resisting chloride-induced degradation at 60–90°C. In nuclear waste reprocessing, hot-finished rods are used to construct evaporator vessels for mixtures of nitric and hydrofluoric acids, utilising the stability of the nickel matrix in oxidising fluorides. The addition of copper (1.5–2.5%) further allows their use in sulphuric acid pickling lines and equipment for phosphate fertiliser production.

Hastelloy G3 Rods/Bars Packaging

Our products are packaged in custom cartons of varying sizes, dependent upon the material dimensions. Small items are securely placed in PP boxes, whereas larger items are packed in custom wooden crates. We strictly adhere to packaging customisation and utilise appropriate cushioning materials to ensure the protection of the items during transportation.

Packaging: Carton, Wooden Box, or Customized.

Please review the packaging details provided for reference.

Manufacturing Process

1.       Testing Method

(1)    Chemical Composition Analysis – Techniques such as GDMS or XRF are employed to verify compliance with the required purity specifications.

(2)    Mechanical Properties Testing – Tensile strength, yield strength, and elongation tests are conducted to quantitatively assess material performance.

(3)    Dimensional Inspection – Thickness, width, and length are measured to ensure adherence to specified tolerances.

(4)    Surface Quality Inspection – Visual and ultrasonic examinations are performed to detect defects such as scratches, cracks or inclusions.

(5)    Hardness Testing – Material hardness is determined to confirm uniformity and mechanical consistency.

Please refer to the testing procedures outlined by SAM for detailed information.

Hastelloy G3 Rods/Bars FAQs

Q1. How does the alloy maintain corrosion resistance in sulphuric acid environments above 60°C, where standard stainless steels fail?

Hastelloy G3’s optimised chromium-molybdenum-copper composition (Cr-22%, Mo-6.5%, Cu-2%) establishes passivation via the formation of Cr/Mo-rich oxide layers. This configuration resists sulphuric acid concentrations ≤50% up to 90°C, whereas 316L stainless steel exhibits significant thinning (>5 mm/year) above 60°C due to the breakdown of chromium-only passive films.

Q2. What maximum chloride concentration and temperature limit prevent stress corrosion cracking in sour gas service?

SCC resistance is maintained in brines containing ≤150 000 ppm chlorides with H₂S partial pressures ≤3.5 bar at temperatures ≤150°C. Beyond these limits, molybdenum depletion at grain boundaries may lead to cracking; this risk is alleviated by microstructural control through solution annealing at 1120°C.

Q3. Does cold working impact corrosion performance in welded assemblies?

Cold-worked sections (>15% reduction) exhibit a 20–30% lower critical pitting temperature in chloride environments. Post-weld solution annealing (1100°C ±15°C) restores a homogeneous microstructure and yields corrosion performance equivalent to that of the base metal.

Related Information

1.       Common Preparation Methods

Hastelloy G3 rods and bars are manufactured through a multi-stage thermomechanical process. The process begins with vacuum induction melting (VIM) of raw materials – primary electrolytic nickel, low-carbon ferrochromium, pure molybdenum, oxygen-free copper and high-purity iron – under an argon atmosphere to achieve precise composition control (Ni-44±1%, Cr-22±0.5%, Mo-6.5±0.3%, Cu-2±0.2%, Fe-balance). The molten alloy is then subjected to secondary refining via vacuum arc remelting (VAR) to reduce interstitial elements (C≤0.015%, O≤30 ppm, N≤100 ppm) and to eliminate macro-segregation. The resulting ingot (typically Ø500–1 000 mm) is homogenised at 1200°C for 8–12 hours to dissolve eutectic phases, followed by hot forging in the γ‐austenite stability range (1050–1150°C) with cumulative reduction ratios ≥4:1 to disrupt the as-cast structure. Subsequent hot rolling at 980–1040°C reduces the cross-section to intermediate blooms (Ø100–200 mm), employing a controlled strain rate (0.1–1 s⁻¹) to prevent edge cracking caused by copper-induced hot shortness.

The semi-finished product undergoes solution annealing at 1120±10°C for 1–2 hours per inch of thickness before being rapidly water-quenched to retain a supersaturated solid solution and inhibit intermetallic precipitation. Cold working (via drawing/swaging) is then performed to achieve the final dimensions, with intermediate soft anneals at 1080°C after a 30–40% cross-sectional reduction to reduce work hardening. Critical microstructural control is achieved by maintaining a grain size of ASTM 5–7 (20–50 μm) through recrystallisation kinetics management and by preventing σ-phase nucleation through limiting exposure to 650–900°C for less than 15 minutes during cooling cycles. Surface finishing involves abrasive belt grinding (Ra ≤1.6 μm) and pickling in HNO₃/HF solutions to remove scale while preserving a substrate free from chromium depletion. Final certification includes eddy current testing for surface defects, ultrasonic inspection for internal discontinuities (with >0.8 mm sensitivity) and validation of corrosion performance according to ASTM G48 Method A (critical pitting temperature ≥85°C in 6% FeCl₃).